Wont be much help i'm afraid as I am a MS free-zone - only got Apple gear.
But... update all the drivers?
What DNS server is it connected to in the settings - is it the same as the other devices?
Try booting it into windoze safe+networking mode and trying speedtests that way, to disable any potentially interfering software - test speeds at...
https://speedtest.samknows.com/
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.